This invention relates to the structural configuration of the cellular portions of a honeycomb structure, and more particularly to an improved cellular structure providing a low bulk modulus and high thermal shock resistance.
Cellular or honeycomb structures made of a ceramic material have application as substrates in catalytic converters for the emissions from internal combustion engines. Due to the extreme temperature variations which such honeycomb structures are subjected to, it is imperative that the structures be provided with the highest thermal shock resistance possible. Naturally, it is desirable to utilize a material having a low coefficient of expansion, and to strengthen the web portions of the structure as much as possible to maintain their integrity. However, in view of the fact that the thickness of such web portions varies between about 0.002 inches and 0.050 inches so as to provide open frontal areas of about 75% or greater, and further in view of the fact that the materials utilized are necessarily of a porous nature so as to increase surface area and facilitate the adhesion of a catalyst thereon, the amount of strengthening and the number of acceptable compositions are severely limited. However, by selecting proper web geometry (i.e. the geometry of the partition members), it is possible to increase the thermal shock resistance by selecting a geometry which will provide the lowest possible bulk modulus and elastic isotropy in transverse planes.
Accordingly, the present invention has helped to overcome the problem of thermal shock in honeycomb structures utilized as catalytic supports in emission control devices, by providing optimum geometry which has low bulk modulus and planar isotropy providing high thermal shock resistance.